Assessment Of Blood Pressure Regulatory Controls To Detect Hypovolemia And Orthostatic Intolerance

Regulation of blood pressure is vital for maintaining organ perfusion and homeostasis. A significant decline in arterial blood pressure could lead to fainting and hypovolemic shock. In contrast to young and healthy, people with impaired autonomic control due to aging or disease find regulating blood pressure rather demanding during orthostatic challenge. This thesis performed an assessment of blood pressure regulatory controls during orthostatic challenge via traditional as well as novel approaches with two distinct applications 1) to design a robust automated system for early identification of hypovolemia and 2) to assess orthostatic tolerance in humans. In chapter 3, moderate intensity hemorrhage was simulated via lower-body negative pressure (LBNP) with an aim to identify moderate intensity hemorrhage (-30 and -40 mmHg LBNP) from resting baseline. Utilizing features extracted from common vital sign monitors, a classification accuracy of 82% and 91% was achieved for differentiating -30 and -40 mmHg LBNP, respectively from baseline. In chapter 4, cause-and-effect relationship between the representative signals of the cardiovascular and postural systems to ascertain blood pressure homeostasis during standing was performed. The degree of causal interaction between the two systems, studied via convergent cross mapping (CCM), showcased the existence of a significant bi-directional interaction between the representative signals of two systems to regulate blood pressure. Therefore, the two systems should be accounted for jointly when addressing physiology behind fall. Further, in chapter 5, the potential of artificial gravity (2-g) induced via short-arm human centrifuge at feet towards evoking blood pressure regulatory controls analogous to standing was investigated. The observation of no difference in the blood pressure regulatory controls, during 2-g centrifugation compared to standing, strongly supported the hypothesis of artificial hypergravity for mitigating cardiovascular deconditioning, hence minimizing post-flight orthostatic intolerance

Analyses of respiratory sinus arrhythmia

Heart rate variability is essential for maintaining the homeostatic balance of the body. It is controlled by the autonomic nervous system. Human biological systems have standard basic characteristics, but varieties of construction and functioning due to genetics, age, sex, and also disease impairment. In addition, they have a complex relationship between systems, such as the nervous system and the cardiorespiratory system. Further analysis of a complex system reveals causes and consequences of its functioning, and helps to detect problems and solve them. Motivated by a better understanding of this relationship I will deepen the analysis of the systems to contribute to the research in this area. The efficiency of the autonomic regulation can be verified by means of respiratory sinus arrhythmia tests observed through electrocardiogram signals ECG and the response of the nervous system can be perceived by electroencephalogram EEG. In this work I present some approaches in the analysis of complex systems such as biological ones. The most relevant contributions of the research are prepared from the knowledge of the cardiorespiratory and nervous biological systems, and the direct relationship between them. The work was concerned with the quality of the instrumentation for biological signal collection and pre-processing for analysis. This stage generated the construction of electrocardiogram equipment. Then, ECG signals were collected from the paralympic boccia team, while the athletes performed their usual breathing exercises to improve concentration and alter heart rates. The electrocardiograms were analysed through the techniques of quantification of recurrence observing the details of the alterations during the exercises. Another approach of the research was the mathematical models of the electrocardiogram. The ECG models were studied and the Kaplan oscillator was chosen, whose model was analysed through bifurcation diagrams and improved in its results. How the athletes change the pattern of the heart and increase the concentration with the exercises. The work passed the EEG analysis stage. Several analyses were performed by linear and non-linear techniques, comparing the signals between the participant with open eyes and closed eyes. A new recurrence analysis technique in the frequency spectrum was generated in this part. The technique presented relevant results to better characterize the signals, can be used to characterize case of depression, and other diseases affecting the central nervous system. Data collection in set of ECG and EEG performing the breathing exercise were performed, the data were analysed by already established techniques and by the recurrence technique created here, we showed that there is a relationship between the heart and brain signals in performing the breathing exercises. All the stages of the work have generated articles which have been published, the first in congresses and the last in specialized journals.Pesquisa sem auxílio de agências de fomentoTese (Doutorado)A variabilidade da frequência cardíaca é essencial à manutenção do equilíbrio homeostáticos do corpo. Esta é controlada pelo sistema nervoso autônomo. Os sistemas biológicos humano têm características básicas padrão, mas variedades de construção e funcionamento devido à genética, à idade, ao sexo, e também comprometimentos por doenças. Além de terem relação complexa entre os sistemas, como acontece entre o sistema nervoso e o cardiorrespiratório. A análise mais aprofundada de um sistema complexo revela causas e consequências de seu funcionamento, e auxilia detectar problemas e solucioná-los. Motivada pela melhor compreensão desta relação vou aprofundar as análises dos sistemas para contribuir com as pesquisas desta área. A eficiência da regulação autonômica pode ser verificada por meio de testes de arritmia sinusal respiratória observada através dos sinais de eletrocardiograma ECG e a resposta do sistema nervoso pode ser percebida pelo eletroencefalograma EEG. Neste trabalho apresento algumas abordagens na análise de sistemas complexos como os biológicos. As contribuições mais relevantes da pesquisa são preparadas partindo do conhecimento dos sistemas biológico cardiorrespiratório e nervoso, e da relação direta entre eles. No trabalho houve a preocupação com a qualidade da instrumentação para coleta de sinais biológicos e do pré-processamento para análise. Esta etapa gerou a construção de um equipamento de eletrocardiograma. E então foram coletados sinais de ECG da equipe paralimpica de bocha, enquanto os atletas realizavam seus habituais exercícios respiratórios para melhorar a concentração e que alteram a frequências cardíacas. Os eletrocardiogramas foram analisados através das técnicas análises de quantificação de recorrência observando os detalhes das alterações durante os exercícios. Outra abordagem da pesquisa foram os modelos matemáticos do eletrocardiograma. Os modelos de ECG foram estudados e foi escolhido o oscilador de Kaplan, cujo modelo foi analisado através de diagramas de bifurcação e melhorado em seus resultados. Como os atletas alteram o padrão do coração e aumentam a concentram com os exercícios. O trabalho passou a etapa de análise do EEG. Foram realizadas diversas análises por técnicas lineares e não lineares, comparando os sinais entre o participante com olhos abertos e olhos fechados. Nesta parte foi gerada uma nova técnica de análise de recorrência no espectro de frequências. A técnica apresentou resultados relevantes para melhor caracterizar os sinais, poderá ser utilizada para caracterizar caso de depressão, e outras doenças que afetam o sistema nervoso central. Coletas de dados em conjunto de ECG e EEG realizando o exercício respiratório foram realizadas, os dados foram analisados por técnicas já consagradas e pela técnica de recorrência aqui criada, mostramos que existe uma relação entre os sinais do coração e do cérebro na execução dos exercícios respiratórios. Todas as etapas do trabalho geraram artigos que foram publicados, os primeiros em congressos e os últimos em revistas especializadas

Recurrence quantification analysis across sleep stages

In this work we employ a nonlinear data analysis method called recurrence quantification analysis (RQA) to analyze differences between sleep stages and wake using cardio-respiratory signals, only. The data were recorded during full-night polysomnographies of 313 healthy subjects in nine different sleep laboratories. The raw signals are first normalized to common time bases and ranges. Thirteen different RQA and cross-RQA features derived from ECG, respiratory effort, heart rate and their combinations are additionally reconditioned with windowed standard deviation filters and ZSCORE normalization procedures leading to a total feature count of 195. The discriminative power between Wake, NREM and REM of each feature is evaluated using the Cohen's kappa coefficient. Besides kappa performance, sensitivity, specificity, accuracy and inter-correlations of the best 20 features with high discriminative power is also analyzed. The best kappa values for each class versus the other classes are 0.24, 0.12 and 0.31 for NREM, REM and Wake, respectively. Significance is tested with ANOVA F-test (mostly p <0.001). The results are compared to known cardio-respiratory features for sleep analysis. We conclude that many RQA features are suited to discriminate between Wake and Sleep, whereas the differentiation between REM and the other classes remains in the midrange